PRAYON PROCESS FOR PHOSPHORIC ACID PRODUCTION

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PRAYON PROCESS FOR PHOSPHORIC ACID PRODUCTION www.prayon.com Our ideas make profitable plants

Transcript of PRAYON PROCESS FOR PHOSPHORIC ACID PRODUCTION

Page 1: PRAYON PROCESS FOR PHOSPHORIC ACID PRODUCTION

PRAYON PROCESS FOR PHOSPHORIC ACID PRODUCTIONCOULEUR 3 DÉGRADÉ

www.prayon.com

Our ideas make profitable plants

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PRAYON PROCESS

PRAYON TECHNOLOGIES: THE REFERENCE IN THE PHOSPHORIC ACID WORLD ........................................................................ 05

THE CHARACTERISTICS OF PRAYON TECHNOLOGIES ................................................................................................................................... 06

A process for each situation .................................................................................................................................................................................... 06

Production-oriented ............................................................................................................................................................................................................. 06

Flexibility .......................................................................................................................................................................................................................... 06

Efficiency ........................................................................................................................................................................................................................... 06

World wide references ................................................................................................................................................................................................ 06

CALCIUM SULPHATE CRYSTALLISATION PHASES .............................................................................................................................................. 07

PRAYON TECHNOLOGIES PROCESSES ...................................................................................................................................................................... 08

First range: process with the first reaction as “dihydrate” ............................................................................................................................ 08

Second range: process with the first reaction as “hemihydrate” ......................................................................................... 08

FEATURES OF PRAYON TECHNOLOGIES DESIGN ............................................................................................................................ 10

Reactor design ................................................................................................................................................................................... 10

Sulphate gradient of the slurry in the attack tank ......................................................................................................................... 10

Low Level Flash Cooler (LLFC) .......................................................................................................................................................... 11

Agitators ............................................................................................................................................................................................... 12

Filters ................................................................................................................................................................................................................................ 13

PRAYON TECHNOLOGIES PROCESSES WITH INITIAL DIHYDRATE REACTION ............................................................ 14

The Mark 4 Dihydrate Prayon Process (DPP) .................................................................................................................................. 14

The Central Prayon Process ............................................................................................................................................................ 15

PRAYON TECHNOLOGIES PROCESSES WITH INITIAL HEMIHYDRATE REACTION .............................................................. 16

Three-crystal process or PH3 (Prayon Hemihydrate 3-crystal) ................................................................................................... 16

Two-crystal process or PH2 (Prayon Hemihydrate 2-crystal) ...................................................................................................... 18

One-crystal process or PH1 (Prayon Hemihydrate 1-crystal) ...................................................................................................... 19

TABLE OF CONTENTS

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PRAYON PROCESS

+ Plants using the Prayon technology

produce over 50% of the world tonnage

of phosphoric acid.

+ Prayon technology and equipment have

been used in over 140 plants located

in over 30 countries.

+ Dozens of different phosphate rocks

have been used in plants from 25 to

2000 mtpd P2O5.

This worldwide success in licensing is not

accidental. Rather, it is based on experi-

ence gained in the area of production.

Behind PRAYON TECHNOLOGIES s.a. is

its parent company Prayon s.a. , a pro-

duction company founded in the 19th

century, which has been manufacturing

phosphoric acid and phosphates for more

than sixty years.

The Prayon Group has 11 production

sites, a total of about 1400 employees,

and an annual turnover of more than

800 million EUR.

PRAYON TECHNOLOGIES mission is to

licence the processes developed in-house,

“by a producer for producers”.

PRAYON TECHNOLOGIES THE REFERENCE IN THE PHOSPHORIC ACID WORLD

For over 60 years, PRAYON TECHNOLOGIES s.a. has been a leader in the licensing of phosphoric acid processes.

PUURS - BELGIUM

ENGIS - BELGIUM

AUGUSTA - USALES ROCHES - FRANCE

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A PROCESS FOR EACH SITUATION

PRAYON TECHNOLOGIES offers 5 dif-

ferent processes, each one with its own

characteristics. This range ensures that

we can provide you with the process

which best meets your requirements.

PRODUCTION-ORIENTED

PRAYON TECHNOLOGIES is a subsidiary

of a manufacturing company. Prior to be-

ing made available on the market, all

technologies and equipment are tested

and proven at our production facilities.

FLEXIBILITY

Plants designed by PRAYON TECHNOLO-

GIES achieve excellent results. They oper-

ate successfully with a large number of

phosphate rocks of various origins and

qualities, including the lowest grades.

Also, if required, the plant can be opti-

mised using phosphate blends.

EFFICIENCY

PRAYON TECHNOLOGIES processes enable

plants to achieve higher efficiency than

their competitors, due to the unique de-

sign of the multi-compartmented reactor.

This design allows the raw materials to

be introduced at the most effective point

in the reactor, yielding optimal results.

WORLD WIDE REFERENCES

These various features have enabled us

to sell a total of over 130 units, includ-

ing more than 50 repeat orders. The lat-

est large scale projects in the world are

based on most advanced Prayon tech-

nologies.

THE CHARACTERISTICS OF PRAYON TECHNOLOGIES

TYPICAL PHOSPHORIC ACID PLANT

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PRAYON PROCESS

CALCIUMSULPHATE CRYSTALLISATION PHASES

The main reaction of phosphate rock with sulphuric acid produces phosphoric acid and calcium sulphate. Depending upon the physical and chemical conditions of the reaction, the calcium sulphate may take the form of dihydrate, α-hemihydrate or anhydrite.

PRAYON TILTING PAN FILTER

100

0

40

60

80

100

120

20

20 30 40 50 60 80

Tem

péra

ture

- °C

Weight percent P2O5 in the acid

HEMIHYDRATE ZONE

DIHYDRATE ZONE

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PRAYON TECHNOLOGIES PROCESSES

FIRST RANGE

Processes with the first reaction as

“dihydrate”

+ With one crystal: “Dihydrate” Prayon

Process or DPP (Mark 4)

DPP DIHY > Dihydrate

+ With two crystals: “Dihydrate then

Hemihydrate” Central-Prayon Process

or CPP

CCP DIHY > HEMI > Hemihydrate

For the past 30 years, Prayon’s licensing

activities have been mainly based on

the DPP - Mark 4 dihydrate process for

phosphoric acid production. Its ability

to efficiently convert various types of

phosphates, its flexibility, its ease of

operation and its low maintenance cost

make it the leading process on the market.

As calcium sulphate is sold at the Prayon

production site at Engis (Belgium), the

purity and quality of the gypsum must be

very high. To fulfil these requirements, the

process used at our unit is the two-stage

dihydrate hemihydrate CPP or CENTRAL-

Prayon Process.

This high-efficiency process (approx.

98.5% cake efficiency) can produce a

relatively strong acid (+/- 35% P2O5).

SECOND RANGE

Processes with the first reaction as

“hemihydrate”

+ With one crystal: “Hemihydrate” Prayon

Process or PH1

PH1 HEMI > Hemihydrate

+ With two crystals: “Hemihydrate” then

“Dihydrate” Prayon Process or PH2

PH2 HEMI > DIHY > Dihydrate

+ With three crystals: “Hemihydrate” then

“Dihydrate” then “Hemihydrate” Prayon

Process or PH3

PH3 HEMI > DIHY > HEMI > Hemi-

hydrate

GAS SCRUBBING TOWER

Prayon Technologies processes can be divided into two groups :

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PRAYON PROCESS

In the late 1970s, the increase of oil prices

put pressure on Prayon to develop higher

strength processes, and two alternatives

were considered. First, the development

of a process with hemihydrate as the first

stage, to produce 43-46% P2O5 acid, or

changing the operating conditions of the

existing Central-Prayon plant to achieve

a product acid strength higher than the

34-36% obtained at that time. This solu-

tion was intended to produce merchant

grade gypsum with similar qualities to

that obtained previously.

A single-stage HH process could not

achieve the gypsum quality required by

the downstream plaster producer, nor a

high enough efficiency to produce phos-

phoric acid economically at the inland

European site.

Although a two-stage hemihydrate-di-

hydrate process would have been more

efficient, the drying stage would have

been costly, compared to the self-drying

characteristics of hemihydrate which

cause the free water to be absorbed

during hydration.

A novel process was then developed, a

Hemi-Di-Hemi process with two recrystal-

lisation stages and two filtration stages.

This process was named the ‘Prayon

Hemihydrate 3-crystal process” or PH3,

and can produce a 46% P2O5 acid with

over 98.5% process efficiency and high

quality calcium sulphate.

Under less stringent conditions, where

gypsum quality is not so critical, the final

stage of the PH3 process can be deleted,

leading to a hemihydrate-dihydrate pro-

cess. This type of process was developed

for licensing purposes and is known as

the “Prayon Hemihydrate 2-crystal pro-

cess” or PH2. This process can yield a

43-46% P2O5 acid and has a process ef-

ficiency of over 98.5%.

In cases where lower efficiencies are ac-

ceptable, the removal of the dihydrate

stage leads to a single-stage hemihydrate

process known as PH1. This can yield acid

39-45% P2O5, with a process efficiency of

up to 95%. If lower strengths are accept-

able, efficiency can be increased. Alterna-

tively, higher strengths can be achieved

at the expense of efficiency.

COMPARISON OF PRAYON PROCESSES (TYPICAL VALUES)

Characteristics of the process Mark 4 CPP PH3 PH2 PH1

Solids product type Dihydrate Hemihydrate Hemihydrate Dihydrate Hemihydrate

Product acid: % P2O5 28.5 34 to 36 43 to 46 43 to 46 39 to 45

Product acid: % SO3 1.5 0.6 to 1.2 0.6 to 1.2 0.6 to 1.2 0.6 to 1.2

Efficiency % 95 to 96 > 98.5 > 98.5 > 98.5 92 to 95

Analysis of the calcium sulphate

(On dry basis 50°C) Free H2O % 18 to 20 14 to 20 14 to 20 16 to 20 14 to 20

(On dry basis 250°C)

Crystal H2O % 20.5 6.2 to 6.5 5.4 to 5.8 18 to 19 6.5

Total P2O5 % 0.8 to 1 0.25 to 0.35 0.15 to 0.25 0.25 to 0.35 1.2 to 1.8

W.S. P2O5 % 0.2 to 0.3 0.1 to 0.15 0.05 to 0.1 0.05 to 0.1 0.2 to 0.3

UNR. P2O5 % 0.05 to 0.1 0.05 to 0.1 0.05 to 0.1 0.05 to 0.1 0.05 to 0.1

Cocryst P2O5 % 0.5 to 0.6 0.1 to 0.2 0.05 to 0.1 0.15 to 0.25 0.8 to 1.4

CaO % 39.8 39.7 40.6 39.8 39

SO3 % 56.9 57 58 57.4 54.9

F% 0.5 to 0.8 0.4 to 0.6 0.1 to 0.2 0.5 to 0.7 1 to 1.2

Na2O% 0.4 to 0.8 0.3 to 0.6 0.1 to 0.2 0.3 to 0.6 1 to 1.2

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FEATURES OF PRAYON TECHNOLOGIES DESIGN

In order to improve the overall performance of phosphoric acid plants, PRAYON TECHNOLOGIES continually updates the design of the equipment used in the process to improve recovery, energy efficiency and the operability of the plant.

REACTOR DESIGN

The PRAYON TECHNOLOGIES reactor

design is unique. It is proven to be highly

reliable. Its multi-compartments design

allows flexibility and easy control of the

sulphate in the attack section, which re-

duces P2O5 losses in the calcium sulphate

and increases the profitability of the unit.

SULPHATE GRADIENT OF THE SLURRY IN THE REACTION TANK

Two types of insoluble losses are pro-

duced during the production of phos-

phoric acid. These are the cocrystallised

and the unreacted losses. The level of

each loss in the gypsum is a function of

several parameters including the sulphate

concentration in the reactor. When the

sulphate concentration of the reaction

slurry is high, cocrystallised losses are

low. When the concentration is low, unre-

acted losses are low. In the reaction tank,

rock is added in the first compartment.

As sulphuric acid is not added to this

compartment, the sulphate concentra-

tion is low. This results in the dissolution

of the rock in a media where unreacted

losses are low. In the compartments 2

and 3, sulphate concentration is gradually

increased to reduce the cocrystallised

losses. The design of the reaction tank

thus minimises the insoluble losses. The

level of sulphate gradient from one zone

to the other can be adjusted depending

upon the process parameters and the

origin of the phosphate rock.

After leaving the attack section, the slurry

flows into the digestion section, where it

will desaturate before being fed to the

filter. Consequently, the gypsum crys-

tals will be large and the slurry will be

desaturated. This feature significantly

reduces filter scaling, which enables the

plant to be run for longer periods be-

tween washes. The increase in stability

improves the overall recovery of the unit

and the onstream time and thus increases

the return on investment.

Optional Sulphate

High Sulphate

Low Sulphate

DigestionR

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PRAYON PROCESS

LOW LEVEL FLASH COOLER (LLFC)

The reaction of phosphate with sulphuric

acid and the dilution of sulphuric acid are

exothermic. To avoid boiling inside the

reactor and to obtain the desired calcium

sulphate crystals (gypsum or hemihy-

drate), the reaction slurry must be cooled.

From the beginning, flash cooling has

been a part of the Prayon process. This

has proved to be more accurately control-

lable than air cooling, especially when

the cooling rate must exceed nominal

capacity.

The principle of operation is the follow-

ing: the LLFC is a vacuum chamber into

which the hot slurry is pumped. The water

in the slurry begins to boil, causing water

to evaporate from the slurry and thus

cooling the slurry. In order to reduce scal-

ing, the temperature difference between

the inlet and the outlet of the LLFC is

low (about 2°C or 4°F). This means that

for efficient cooling the flow through the

LLFC must be very large. This is ensured

by a high flow rate axial flow pump with

a low head and a low power consumption.

DIGESTION TANKS AND LOW LEVEL FLASH COOLER

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AGITATORS

Agitation is a key factor in chemical pro-

cesses as it improves the mass transfer of

the reagent and crystallisation conditions

in the reaction slurry.

During the reaction period of phosphoric

acid production, agitation is used for the

following purposes:

+ To keep the solids suspended.

+ To renew the liquid layer (reagent) on

the phosphate grains.

+ To break the foam on the surface of

the reactor.

To be economical this process needs to

be performed with as low a power con-

sumption as possible. PRAYON TECH-

NOLOGIES has developed a special type

of agitator to fulfil these requirements.

The bottom blade is a helicoidal shape

to ensure a high pumping rate. It keeps

solids suspended and the compartment

clean. The middle blade is a pitched blade

with a pumping effect. It also generates

shear, which improves the mass transfer

and the incorporation of the reagents.

The top blade is a vertical turbine blade

with an antifoaming effect (achieved by

splashing liquid on the reactor surface)

and helps incorporate reactants fed to

the surface of the reactor.

In the digestion section, strong agitation

is no longer necessary. Only helicoidal

blades with low specific power consump-

tion are used.

For a few years now, PRAYON TECHNOL-

OGIES has been using a Computerized

Fluid Dynamics software in order to fur-

ther improve the design of its agitators.

PRAYON REACTION TANK AGITATOR

FEATURES OF PRAYON TECHNOLOGIES DESIGN

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PRAYON PROCESS

FILTERS

Depending upon the customer’s require-

ments, PRAYON TECHNOLOGIES offers

tilting pan filter or belt filter technology.

The Prayon tilting pan filter is the best

known filter in the phosphoric acid indus-

try. Its washing efficiency is the highest

of all the filters available on the market.

Recent developments in filter technology,

such as the “fast-drain” cell, the central

valve, inverting track design, etc., have

improved its operability, reduced main-

tenance cost and increased the filtering

surface to the total surface ratio.

The Prayon belt filter also offers consid-

erable advantages: excellent washing

efficiency, low power consumption, easy-

to-clean vacuum box and accessibility to

all internal parts.

BELT FILTER

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PRAYON TECHNOLOGIES PROCESSES WITH INITIAL DIHYDRATE REACTION

THE MARK 4 DIHYDRATE PRAYON PROCESS (DPP)

This process has undergone major in-

novation every ten years or so, up to the

achievement of the highly efficient Mark

4 version, which is a favourite with pro-

ducers due to its reliability, simplicity of

operation and the use of tried-and-tested

equipment.

THE MAIN CHARACTERISTICS OF THE PROCESS ARE

+ low investment and running costs

+ the ability to process all types of phos-

phates (sedimentary and igneous)

+ accepts phosphate slurry feeding (wet

grinding)

+ water balance is easy to control (recy-

cling of pond water, reduction and/or

elimination of liquid effluent)

+ dihydrate route

+ good P2O5 recovery

RECOMMENDED FOR LOCATIONS

+ with low to medium cost rock

+ with low-cost energy (steam)

+ with gypsum disposal possibility

PhosphateFlash Cooler

Filter

Water

Phosphoric Acid 28 to 30% P2O5

CalciumSulphateDihydrate

H2SO4

Reaction

Recycled Acid

Digestion

DIHYDRATE

Vacuum

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PRAYON PROCESS

THE CENTRAL-PRAYON PROCESS

The Central-Prayon Process was developed

to produce a calcium sulphate (phospho-

gypsum) which could replace the natural

gypsum in different applications.

This process is a dihydrate-hemihydrate

process. During the first stage, slurry con-

taining dihydrate crystals is produced. From

that flow, the quantity corresponding to the

product acid is sent to storage, the remaining

quantity being sent with the solids to the

conversion tank. In this reactor, sulphuric

acid and steam are added to transform the

dihydrate solids into hemihydrate liberating

most of insoluble losses. The slurry produced

is then filtered and the cake washed. All

filtrates from the second filter are recycled

to the reaction tank, while solids can be

neutralised and used as a raw material for

gypsum products.

THE MAIN CHARACTERISTICS OF THIS PROCESS ARE

+ it produces a higher acid strength than

DPP with much higher P2O5 recovery

+ it can process both types of phosphates:

sedimentary and igneous

+ it produces CaSO4.1/2H2O which is self-

drying due to its chemical properties

and is purer than dihydrate, and can

therefore be used directly as a merchant

grade raw material (phosphate selec-

tion may be important)

RECOMMENDED FOR LOCATIONS

+ with medium - high-cost rock

+ with high-cost energy

+ with disposal limitation and/or with a

potential market for this purer gypsum

PhosphateFlash Cooler

Steam

Water

Phosphoric Acid 32 to 36% P2O5

Pure CalciumSulphateHemihydrate

H2SO4

Reaction

Recycled Acid

Digestion

DIHYDRATE HEMIHYDRATE

Vacuum

Separation filter

Hemihydrate conversion

Hemihydrate Filter

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PRAYON TECHNOLOGIES PROCESSES WITH INITIAL HEMIHYDRATE REACTION

As energy costs weigh increasingly heavily, it may be worth producing a more highly concentrated acid directly from the filter, provided this is permitted by the water balance.

To fulfil this requirement, as well as that

of producing a self-drying hemihydrate,

Prayon has developed the PH3 process.

This is a three-crystal process that yields

a high P2O5 acid and a phosphogypsum

that can be used as a base for construc-

tion materials. Once this process had

been developed, we felt it could be sim-

plified by deleting stages to fit to certain

client requirements. This led to the de-

velopment of two further hemihydrate

processes.

To achieve a successful engineering pack-

age for high-strength processes, Prayon

was able to rely on both:

hardware: many years of experience in

the operation and engineering of equip-

ment (reaction tank, agitators, cooling

equipment, filters...)

software: our expertise with multicrystal

process operation, our in-depth knowledge

of phosphate behaviour and the ability to

design successful industrial units based

on pilot-plant data.

Phosphate

Flash Cooler

Steam Water

Phosphoric Acid 40 to 46% P2O5

Pure CalciumSulphateHemihydrate

H2SO4

Reaction

Recycled Acid

Digestion

DIHYDRATE HEMIHYDRATEHEMIHYDRATE

Vacuum Vacuum

Separation filter

Dehydration tanks

Hemihydrate Filter

Vacuum

Flash Cooler Optional

Flash Cooler

Hydratation tanks Seal tanks

THREE-CRYSTAL PROCESS OR PH3 [ PRAYON HEMIHYDRATE 3-CRYSTAL ]

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PRAYON PROCESS

This process is divided into three stages:

Stage 1 α-hemihydrate attack-filtration:

The phosphate rock is digested in con-

ditions which ensure the production of

43-46% P2O5 acid with low SO3 (± 1%).

The control of the operating conditions

allows the production of hemihydrate

which will filter rapidly and lend itself to

full rehydration during the second stage.

Stage 2 Conversion of α-hemihydrate to dihydrate:

By changing the operating conditions (tem-

perature, % P2O5, % SO3), α-hemihydrate

is converted into dihydrate in order to

achieve a first purification, especially of

unreacted and cocrystallised P2O5.

Stage 3 Conversion of dihydrate to α-hemihydrate

and final filtration:

Operating conditions are modified to trans-

form the dihydrate into α-hemihydrate.

The slurry produced is then filtered. This

step is similar to the second part of the

Central-Prayon Process and aims at produc-

ing a high purity calcium sulphate which

is separated by filtration and washed with

water. If requested, the hemihydrate can be

processed further (neutralisation, rehydra-

tion to produce a dry solid) to produce a

substitute for natural gypsum.

THE MAIN CHARACTERISTICS OF THE PROCESS ARE

+ high P2O5 recovery (> 98.5%)

+ high-strength phosacid

+ self-drying gypsum

The last two points reduce energy con-

sumption.

RECOMMENDED FOR LOCATIONS

+ with medium - high-cost rock

+ with high-cost energy

+ without easy gypsum disposal

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PRAYON TECHNOLOGIES PROCESS WITH INITIAL HEMIHYDRATE REACTION

TWO-CRYSTAL PROCESS OR PH2 [ PRAYON HEMIHYDRATE 2-CRYSTAL ]

After the first reaction in hemihydrate

mode, the product acid is separated as

a 46% P2O5 with low SO3 content. The

remaining α-hemihydrate, washed with

recycled liquor, is further processed

with sulphuric acid in conditions in

which α-hemihydrate is unstable and

recrystallises as gypsum, releasing

cocrystallised and unreacted P2O5.

THE MAIN CHARACTERISTICS OF THE PROCESS ARE

+ high-strength phosacid

+ high P2O5 recovery (> 98.5%)

RECOMMENDED FOR LOCATIONS

+ with medium - high-cost rock

+ with high-cost energy

+ with easy gypsum disposal

Phosphate

Water

Phosphoric Acid 40 to 46% P2O5

Pure CalciumSulphateDihydrate

H2SO4

Reaction

Recycled Acid

Digestion

DIHYDRATEHEMIHYDRATE

Vacuum Vacuum

Separation filter

Dihydrate Filter

Vacuum

Flash Cooler Optional

Flash Cooler

Hydratation tanks

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PRAYON PROCESS

ONE-CRYSTAL PROCESS OR PH1 [ PRAYON HEMIHYDRATE 1-CRYSTAL ]

The reaction takes place in two stages.

The first stage takes place with a low but

positive sulphate level, while the second

stage operates with a higher sulphate

level. Perfect sulphate and temperature

control permit the filtration of a slurry

containing a highly stable hemihydrate

with low scaling properties.

THE MAIN CHARACTERISTICS OF THE PROCESS ARE

+ simple and low-cost process

+ high-strength acid

RECOMMENDED FOR LOCATIONS

+ with low-cost rock

+ with low-cost sulphuric acid

+ with high-cost energy

+ where gypsum disposal is not a problem

Phosphate

Water

Phosphoric Acid 39 to 45% P2O5

CalciumSulphateHemihydrate

H2SO4

Reaction

Recycled Acid

Digestion

HEMIHYDRATE

Vacuum Vacuum

Filter

Flash Cooler Optional

Flash Cooler

Page 20: PRAYON PROCESS FOR PHOSPHORIC ACID PRODUCTION

Rue Joseph Wauters, 144B-4480 Engis

Tel. +32 (0) 4 273 93 41Fax. +32 (0) 4 275 09 09mail. [email protected]

PRAYON TECHNOLOGIES S.A. LICENSING DIVISION OF PRAYON

www.prayon.com

PROCESS LICENSING

CONSULTING

+ Phosphoric acid production

+ Phosphoric acid concentration

+ Fluorine recovery

+ Gas scrubbing

+ Phosphoric acid purification

+ Gypsum purification

+ Uranium extraction from phosphoric acid

If requested by the customer, Prayon

Technologies can provide the following

services:

+ Technical support for existing units

+ Training of operators

+ Phosphate rock evaluation